The deleted-simple socle class #
At a positive new mesh, the torsion-free quotient of the ambient Auslander--Reiten middle has a simple submodule supported at the deleted primitive idempotent. This produces the manuscript's nonzero map from the deleted simple and hence a nonzero connecting extension class.
Maps from the primitive projective to an AeA-annihilated module are
zero.
The primitive projective maps one-dimensionally to the ambient AR middle at a new endpoint.
In the fixed ambient decomposition of the AR middle, the sum of all primitive coordinates is one.
Exactly one displayed ambient middle summand has nonzero primitive coordinate, and that coordinate is one.
The unique displayed ambient middle summand carrying the deleted primitive coordinate.
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The primitive coordinate of every displayed middle summand, relative to the exceptional index.
The label of the unique ambient middle summand containing the deleted primitive coordinate.
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The manuscript's exceptional middle summand Y.
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The exceptional summand has primitive coordinate one.
The exceptional summand is not an A/AeA-module.
Every other displayed ambient middle summand is an A/AeA-module.
The direct sum of all displayed ambient middle summands except the
exceptional summand Y.
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The selected ambient decomposition splits the AR middle as
V₀ ⊕ Y.
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Every summand of V₀ is an A/AeA-module, so V₀ itself is
annihilated by AeA.
Applying primitive torsion to the manuscript split gives
R(V) ≅ V₀ ⊕ R(Y): torsion fixes the killed complement and acts only on
the exceptional summand.
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The canonical inclusion of the exceptional summand into the selected ambient decomposition.
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The exceptional summand inclusion is monic.
Positivity forces Hom_A(S_e,Y)=0 for the exceptional summand.
A module receiving a one-dimensional Hom space from the primitive projective has nonzero primitive torsion-free quotient.
The exceptional summand's canonical torsion sequence
0 -> R(Y) -> Y -> T_Y -> 0.
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The exceptional summand's torsion sequence is short exact.
The exceptional torsion-free quotient T_Y is nonzero.
The connecting map
Hom_A(S_e,T_Y) -> Ext¹_A(S_e,R(Y)).
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At a positive mesh, the exceptional-summand connecting map is injective.
A chosen simple submodule of a nonzero primitive torsion-free quotient.
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The chosen torsion-free socle submodule is simple.
The chosen simple submodule, bundled as a finitely generated ambient right module.
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The bundled socle object remains simple.
The chosen simple submodule cannot be an A/AeA-module, because the
torsion-free quotient has no nonzero AeA-annihilated submodule.
The deleted simple occurs in the socle of the torsion-free quotient:
there is a nonzero map from S_e.
A fixed nonzero deleted-simple map into the exceptional torsion-free
quotient T_Y.
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The fixed socle map is nonzero.
The extension class obtained by applying the torsion-sequence connecting map to the fixed deleted-simple socle map.
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At a positive new mesh, the selected connecting extension class is nonzero.
Some displayed indecomposable summand of R(Y) receives a nonzero
component of the positive connecting class.
A fixed summand index of R(Y) on which the connecting class is
nonzero.
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The nonzero Ext component at the fixed summand index.
The quotient label Z selected by the nonzero positive connecting
component.
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The selected positive source is ambient noninjective, as witnessed by its nonzero degree-one Ext component.
The positive pair source bundled with the noninjectivity needed to form its inverse Auslander--Reiten translate.
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The ambient label τ_A⁻¹ Z used to read the sign of the positive
gaining pair selected at a new mesh.
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The selected positive gaining-pair source has positive source marker:
there is a nonzero map τ_A⁻¹ Z ⟶ S_e.
The selected label occurs with positive multiplicity in R(Y).
At a positive new mesh, the selected quotient label occurs strictly
more often in the relative middle R(V) than in the ambient AR middle
V.